Method of gas stabilizing a supersonic inlet



Sept. 26, 1961 L7 R. WOODWORTH 3,001,364

METHOD OF GAS STABILIZING A SUPERSONIC INLET Filed July 18, 1958 F I6. I

26 2 2 24 Z Q J F I G. 2

INVENTOR.

L EE R. WOODWORTH ATTORNEXS United States Patent 3,001,364 METHOD OF GAS STABILIZING A SUPERSONIC INLET Lee R. Woodworth, Calabasas, Califi, assignor to the United States of America as represented by the Secretary of the Air Force Filed July 18, 1958, Ser. No. 749,572 3 Claims. (Cl. 60--35.6)

This invention relates to supersonic inlets and is more particularly concerned with a novel method for improving the pressure recovery of such inlets.

In the early development of ramjet engines a circular hole at the forward end of the engine housing was provided for the intake of air at supersonic speeds. This was found to result in discontinuous compression and considerable power losses due to isenthropic compression and to plane normal shock. In efforts to reduce or eliminate these effects a compression nozzle has been suggested in which a pointed, rotary-symmetrical body is positioned at the center of the engine air intake surrounded by a casing or jacket spaced from its surface adjacent its zone of largest diameter. Thus, an annular port defined by the substantially conical surface of the body and the circular inner edge of the outer jacket was provided. At speeds corresponding to a Ma'ch co-efficient of 3.0, the blunt front edge of the jacket causes large air resistance. It also builds up over-pressure which impedes the satisfactory flow of air into the annular compression nozzle intake port while the high angle of deflection of the air entering the port creates a high resistance against the jacket and interferes with the compression procedure. On the other hand, when the front edge of the jacket is at a smaller angle to the axis of symmetry, insufficient compression of the air is effected.

In order to overcome the above inadequacies, my invention contemplates the complete elimination of the central cone, and substitutes a series of stabilizing gas inlets.

It is accordingly the principal object of this invention to provide an improved method of increasing the pressure recovery of supersonic inlets.

More specifically, it is the object of this invention to improve pressure recovery in such inlets by injection of stabilizing gas or fluid into the intake.

The above, and still further objects, advantages and features of my invention will become apparent upon consideration of the following detailed description thereof, especially when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a schematic illustration of central cone type inlet showing the shock wave pattern; and

FIGURE 2 is a schematic illustration to a supersonic inlet incorporating the teachings of my invention.

Most of the present supersonic air inlets now employed are of the external compression type which attempt to minimize losses through external shock systems. Such an inlet is shown in FIGURE 1. The cylinder formed by the cowling has a cone or contoured spike 12 centrally positioned in its inlet end 14. The cone or spike 12 may be mounted in any suitable fashion. When in use, the oblique and normal shock waves, 16 and 18 respectively, act against the inlet end 14 as shown. This type of system accepts compression shocks as inevitable. It then proceeds to attempt to minimize the losses occasioned thereby. At high flight speds of Mach 3.0 or above, the above system leaves much to be desired since the pressure recovery is quite low, in the vicinity of 50 to 70 percent.

Generally, my invention employs an internal compres- 3,001,364 Patented Sept. 26, 1961 sion system as seen in FIGURE 2. A cylindrical cowling 22 has an inlet end 24. A conventional type throat 26 is formed within said cowling, and the downstream end of said throat leads to the engine. The latter may be either of the ramjet or turbojet type. The theoretical performance of this type of inlet is well known. Although theoretically capable of high efficiency, it presents a problem in actual operation since the normal shock which forms at the face must move inside the inlet and become vanishingly small at the throat. This normal shock wave will not enter unless M is well above the proper design value for the inlet. Even after entry has been made, it will tend to pop out at the slightest provocation.

The method of this invention solves this problem by injecting a stabilizing gas into the suspersonic inlet. The particular gas used must be of low molecular weight and have high specific heat values. Both hydrogen and helium have been found suitable for this purpose. The stabilizing fluid is injected into the turbulent boundary layer air at the inlet through a plurality of openings 28 in such a manner that the shock front is induced to enter said inlet and become stabilized. The openings 28 must be positioned between the plane of the inlet end 24 of the cowling 22 and the plane of the throat 26.

The action of the fluid is two-fold; it first cools the inlet air and thus increases the density of the turbulent air at the injection points. This is equivalent to increasing the inlet area. Secondly, the low molar value of the injected fluid tends to reduce the local Mach number at the injection station. The overall effect of these actions is to achieve efficient and effective operation of the supersonic inlet.

It is to be understood that the above described arrangement is merely illustrative of the principles of the invention. Numerous other arrangements may be devised by those skilled in the art without departing from the spirit and scope of my invention.

What is claimed is:

1. A method for improving the operation of supersonic air inlet having a wall adjacent to which there is turbulent boundary layer flow, said wall defining an entrance to said inlet, said method comprising the steps of cooling at least a portion of the air which flows into said inlet and of simultaneously reducing the Mach numher in said turbulent boundary layer, said cooling and said reducing of the Mach number being achieved by injecting a stabilizing gas having lower temperature and molar value than said air.

2. A method as defined in claim 1 wherein said stabilizing gas is hydrogen.

3. A method as defined in claim l wherein said stabilizing gas is helium.

References Cited in the file of this patent UNITED STATES PATENTS 2,602,289 Anxionnaz et al July 8, 1952 2,864,236 Toure et a1. Dec. 16, 1958 2,880,579 Harshman Apr. 7, 1959 2,957,308 McMurtrey Oct. 25, 1960 FOREIGN PATENTS 439,805 Great Britain Dec. 6, 1935 857,780 France Apr. 26, 1940 OTHER REFERENCES Gas Tables by Keenan and Kaye, copyright 1948, published by John Wiley and Sons, Inc., New York (pages 148-151, 209 and 210 relied on). 

